Information about latency of a fronthaul transmission link, or in other words the fronthaul link latency, is essential for modern radio systems, such as 3rd Generation Partnership Project (3GPP) Universal Mobile Telecommunications System (UMTS) or 3GPP Long Term Evolution (LTE) in order to be able to coordinate, e.g., multi antenna systems or to set and/or adjust radio link parameters to optimum levels. Latency is a time interval between the transmitter sends a signal and arrival of the signal at the receiver. For example network latency is measured either as one-way or round-trip delay. The fronthaul transmission link is the link between a base station baseband or digital unit to a remote radio head and antenna.
For example, the performance of wireless Multiple Input Multiple Output (MIMO) is strongly relying on close alignment and phase-coordinated transmission and reception of the individual antenna signal over the fronthaul transmission link. A misalignment or timing uncertainty in radio systems is expressed as Timing Alignment Error (TAE). Maximum allowable TAE varies between about 30 ns and 1 μs depending on the specific requirement for the specific fronthaul case, e.g. Radio Base Station (RBS) antenna, RBS and several MIMO antenna, different RBS/LTE-Time Domain Duplexing. Each km of standard optical cable introduces a transmission delay of 5 μs. Therefore, a problem is that even short transmission cables will result in violation of radio standard requirements and, without latency compensation, render the application of fiber in the fronthaul pointless.